Public school teachers are public servants whose work product just got a whole lot more public.

Yesterday,the city Department of Education released ratings on 18,000 teachers, based on standardized student-assessment results in English and math over a period of three school years ending in 2010.

The release comes after 18 months of unsuccessful litigation by the United Federation of Teachers, which sued to block the release of the Teacher Data Reports when the media requested the information.

Throughout, the Bloomberg administration properly defended the right of the public to have the names and ratings of teachers.Sensitive to the power of the teachers union, schools Chancellor Dennis Walcott now is trying to ease some of the concerns of teachers by saying that the ratings are only a “snapshot” and should not be used in “isolation.”

UFT President Michael Mulgrew is furious, having failed first to avoid meaningful teacher evaluations and now to block the public release of those ratings.After using money taken from teachers’ salaries to pay lawyers to litigate in vain, he’s now using union funds to wage a media ad campaign attacking the city Department of Education and the rating system.

Mulgrew screeches that the ratings are flawed, based on “bad tests, a flawed formula and incorrect data” that will mislead the public about teachers’ effectiveness. In typical obstructionist fashion, of course, no promise of the public release of results of a better-designed rating system, such as the one recently approved by the state, accompanies his complaints.

Unlike Mulgrew, former UFT chief Randi Weingarten endorsed the Teacher Data Report system when it was first devised in 2008 — particularly noting the value such feedback on teacher performance can have: “This can be used to inform instruction and advance it.”

While Weingarten held firm that this data on whether teachers advanced their students’ learning (an element many consider the core component of a teacher’s job) shouldn’t be used in job-performance evaluations, she acknowledged that “this information can be a powerful instructional tool.”

No rating system will be perfect from the perspective of everyone involved.After all, being able to use the tenure system to guarantee yourself a job for life without anyone knowing whether you actually perform effectively is a pretty sweet deal. But the Department of Education, with the full backing of the mayor, has won a victory for parents, children and school administrators trying to improve the quality of public education.

At the state level, similar important reforms are coming thanks to efforts by Gov. Cuomo and the state Education Department’s leaders to require that a meaningful teacher-evaluation system be put in place in every public-school district in New York.

No one wants to see any teacher unfairly rated, much less unfairly criticized, for his or her performance.But the union’s complaints would have more credibility if it weren’t for the long history of the UFT (and its statewide parent union, NYSUT) in resisting greater accountability and transparency in public schools.

New York’s teachers unions have opposed nearly every attempt to:

* Close persistently bad schools.

* Reform the process for removing poorly performing teachers.

* Institute a “last in, first out” layoff policy to retain superior teachers with less seniority.

* Set up a merit-based compensation system to pay great teachers more than their not-so-great peers.

* Create alternative public schools, such as charter schools.

* And on and on.

Teacher-rating systems are important. Schooling consumes billions of public dollars each year, and parents and taxpayers have a right to know how well teachers are doing to improve the education of children. The Teacher Data Reports are a big step forward in illuminating teacher performance.

No one, including the rating system’s biggest advocates, is opposed to improving the quality of such evaluations. Rather than continuing to object to the fact that teachers are evaluated and — gasp! — that parents will be able to see whether their children’s teachers are doing their jobs well, the UFT and the state union should note that a new rating system already has been agreed upon by the unions and the state’s education policymakers. Rather than a media attack campaign, they might devote resources to professional development and teacher education to improve the quality of classroom instruction.

And to maintain at least a shred of credibility, the unions need to get serious about removing poor-performing teachers rather than protecting them. After all, it’s supposed to be about the students, right?

Brian Backstrom is the vice president at The Foundation for Education Reform & Accountability, an independent, nonprofit, research organization dedicated to improving education in New York by promoting accountability, innovationand school-choice efforts across the state.